FuelCell Energy marks its 50th anniversary on Thursday, with the company the oldest, continually operating fuel cell manufacturer in the world.

Founded in Danbury in March 1969 as Energy Research Corp., FuelCell’s devices create electricity by a chemical process, akin to a battery but requiring a steady supply of hydrogen as fuel. Fuel cells do not produce noxious emissions like traditional power plants, qualifying them for green energy subsidies from governments.

“Our (company’s) past and present is dominated by employees and investors that are here because they want to be part of something special and meaningful and lead the way globally in clean, continuous energy production,” stated CEO Chip Bottone, in a letter to FuelCell employees provided Hearst Connecticut Media on Wednesday evening.